1. Field of the Invention
The present invention relates to a method for monitoring and controlling an appropriate cell flow rate for an ATM (Asynchronous Transfer Mode) switch.
2. Related Arts
An ATM switch receives a cell in a format consisting of a 5-byte header and a 48-byte payload, as is shown in FIG. 9, and selects and outputs a path in the ATM switch, based on a virtual channel identifier (VCI).
As is shown in FIG. 10, such an ATM switch 1 is connected via a transfer channel to users 31 through 3n by a UNI (User-Network Interface), or is connected to another ATM switch 11, which is connected to a user 50 via a transfer channel by an NNI (Network-Node Interface).
In FIG. 10, an ATM switch 1 has input interface circuits 21 through 2n, an ATM switch unit 10 and an output interface circuit (not shown).
The input interface circuits 21 through 2n each include a transfer channel end section 210, for receiving a cell across the transfer channel; a cell flow rate monitor section (UPC: Usage Parameter Control) 211; a performance monitor section (OAM: Operations, and Maintenance) 212; and a header converter (HCV) 213, for converting a VCI that is employed for the input transfer channel into a VCI that is employed for the ATM switch 1 and an output transfer channel.
In order to increase the efficiency of the cell processing by the ATM switch, a cell transmission rate is set and declared in advance between a network manager and a subscriber before the operation. Cells are output by the subscriber at the declared transmission rate.
However, sometimes the transmission rate fluctuates, depending on the time period, and the cells are transmitted at a transmission rate different from the declared transmission rate. Therefore, the UPC 211 monitors the traffic from the subscriber, i.e., the flow rate for the cells that are transmitted. When the flow rate exceeds the cell transmission rate that was set in advance, the UPC 211 performs conformance.
The OAM 212 monitors the occurrence of failure in a network and the performance. When an abnormality is detected, the OAM 212 makes a detour in route, switching the line to a protection line, etc. The detection of failure and the monitoring of the performance is performed by monitoring an OAM (Operations, and Maintenance) cell that is transmitted together with a normal cell.
In FIGS. 11 through 13 are shown flow charts of processing, which is specified by the advisory or the committee, for performing different conformance test components by using a CLP (Cell Loss Priority) value.
The CLP (Cell Loss Priority) value of a cell is indicated by one bit that is present in the header portion of the format shown in FIG. 9. Therefore, the CLP value is "1" or "0." A CLP value of "1" indicates that, when a traffic congestion occurs, the cell has the highest abandonment priority.
The control of the UPC 211 relative to the CLP value is designated by the ITU-T advisory, etc. In FIGS. 11 and 12 are examples described in ITU-T advisory FIG. 8/I.371; FIG. 11 is an example with no tagging option, and FIG. 12 is an example with a tagging option. The tagging is the control to input a cell without abandoned to the ATM switch 1, and set the CLP value as CLP=1 which means the cell may be abandoned, if necessary due to congestion.
In FIG. 11, the processing for an input cell branches depending on its CLP value (step S01). When CLP=0, processing for a test component C.sub.0 is performed (step S02), and after summing processing is emerged (step S03), processing for a test component C.sub.0+1 is performed (step S04). When CLP=1, only the processing for the test component C.sub.0+1 is performed.
For the conformance test, cells are abandoned as needed. Then, a parameter for a pertinent conformance component for updated (step S05). In FIG. 11, the parameter of the conformance test CLP=0+1 (step S05) are updated.
In FIG. 12 is shown a conformance test having a tagging option. When the result of the processing for test component C.sub.0 (step S02) is non-conformance, the processing is changed with CLP=1 (step S06).
In FIG. 13 is shown an example described in FIG. II-1 of the ATM Forum Technical Committee Report. This is the connection for which only CLP=0 is used, and two conformance tests, T.sub.0 (test for PCR: Peak Cell Rate) and T.sub.s0 (test for SCR: Sustainable Cell Rate), are performed.
In this connection, either the cell with CLP=1 is abandoned, or some conformance test is performed for that cell. The conformance test in this case can currently have six or more different patterns, such as the leaky bucket algorithm and the virtual scheduling algorithm.
When a large number of cells are temporarily transmitted at a rate exceeding that declared by a subscriber and causes a traffic congestion, these cells overflow from a bucket. According to the leaky bucket algorithm, the traffic is monitored using the depth of a bucket that leaks a predetermined amount, and the cells that overflow the bucket are regarded as illegal cells.
More specifically, according to the leaky bucket algorithm, a counter is used as a bucket. When a cell is received, the counter increments a value, and counts down in a constant period, so that the bursting of cells and the average cell flow rate are monitored.
Since a plurality of types of conformance tests are set for each connection in accordance with the example represented by the advisory or the committee report, various conformation tests must be performed using the same interface.
When the processing in FIGS. 11 through 13 described in the advisory is built using the same architecture, it will be very complicated.
When these conformance tests are to be performed by switching modes, the tests will be less flexible because there may still be an alteration and an addition to the advisory.